1. Technical Field
The present disclosure generally relates to systems, methods and articles for cooling components.
2. Description of the Related Art
Modern aircraft include generators that generate power during flight and provide the generated power to onboard aircraft electric power systems. The generators utilize rotation of the aircraft engine to generate AC power using various power generation techniques. Power generated in this manner may be 230V 400 Hz AC power, for example. While the aircraft is on ground, aircraft engines can be turned off, the onboard generator ceases generating power, and the onboard electric system instead may receive AC power from a ground cart. Power provided from the ground cart may be 115V 400 Hz AC power, for example.
While the power sources provide AC power, aircraft components often require DC power instead of AC power. AC-DC power conversion may be accomplished with a plurality of diode pairs, where each pair is connected to a different phase of the AC input, to provide a rectified DC output. However, this type of AC-DC conversion may lead to substantial current harmonics that pollute the electric power generation and distribution system. To reduce current harmonics, multi-phase autotransformers may be employed to increase the number of AC phases supplied to the rectifier unit. For example, in an 18-pulse passive AC-DC converter, the autotransformer is used to transform three-phase AC input, whose phases are spaced at 120°, into a system with nine phases spaced at 40°. This has the effect of reducing the harmonics associated with the AC-DC conversion.
A transformer typically includes windings of electrically conductive material such as wire. The windings are spaced sufficiently close together such that an electrical current flow through one winding will induce an electrical current to flow in another winding when connected to a load. Windings through which current is driven are typically denominated as primary windings, while windings in which current is induced are typically denominated as secondary windings. The transformer also may include a core, for example a magnetic or ferrous core around which the windings are wrapped.
A rectifier typically includes a plurality of diodes or thyristors configured to convert an AC signal to a DC signal. For example, a full-bridge rectifier may be employed to convert an AC signal to a DC signal. Additional devices may be employed to provide power conditioning, such as inter-phase transformers, balancing inductors, inter-phase reactors, filters, etc.
In many applications, transformer size and/or weight are important factors in realizing a practical and/or commercially successful device. For example, power converters for use in avionics typically must be lightweight and may need to occupy a small volume. Such applications, however, typically require high performance, such as high-current, low noise power conversion. Many applications may additionally, or alternatively, require low-cost power converters. Cost may be dictated by a number of factors including type of materials, amount of materials, and/or complexity of manufacture, among other factors.
Many electromagnetic devices or components generate heat during use and require cooling to keep the temperature of the device or surrounding environment sufficiently low. Certain devices, including transformers and inductors, include current carrying windings that generate a large amount of heat that needs to be dissipated. However, because the windings are often tightly wound and may be coated with an insulating material, heat generated internally must either transfer across several layers of insulation, travel through the core material (which may exhibit poor thermal conductivity) or travel along a winding conductive path and into the wiring or bussing connected to the device. None of these heat flow paths is particularly efficient.
Heat dissipation becomes increasingly important when electromagnetic devices operate at high power levels. High temperatures generated by these devices limit the power levels at which the devices can operate. Such temperature limits thus may also adversely affect the volumetric and weight performance of equipment incorporating the electromagnetic devices. This is especially true in high power density equipment operating in high ambient temperature or in applications where active cooling may be required, such as in aerospace applications. Heat sinks are known for cooling electronic equipment, but are generally only useful for removing heat from exposed surfaces of an electromagnetic device.